1. Field of the Invention
The present invention relates to a vehicular remote control system that controls the operation of a device on a vehicle by carrying out communication between a portable device and the vehicle using two types of radio waves having different frequencies.
2. Description of the Related Art
A vehicular remote control locking/unlocking system is known from Japanese Patent Application Laid-open No. 10-176448, which discloses a system in which an LF signal at a few hundred kHz is used as an ID signal request-to-send signal, which is transmitted from a vehicle to a portable device. Furthermore, the known system uses an RF signal at a few hundred MHz as an ID signal, which is transmitted from the portable device to the vehicle in response to the ID signal request-to-send signal.
Another vehicular remote control system is known from Japanese Patent Application Laid-open No. 2000-104429, which discloses a system having an ID signal request-to-send signal that is transmitted from a vehicle to a portable device. In the disclosed system, when an ID signal transmitted from the portable device to the vehicle in response to the ID signal request-to-send signal is authenticated, an interrogation signal is transmitted from the vehicle to the portable device. Accordingly, when a response signal transmitted from the portable device to the vehicle in response to the interrogation signal is authenticated, operation of a device on the vehicle is permitted.
The system disclosed in Japanese Patent Application Laid-open No. 2000-104429 has the problem wherein if a transmitter which transmits the interrogation signal or a receiver which receives the interrogation signal breaks down, transmission and reception of the interrogation signal become impossible and the entire vehicular remote control system is rendered inoperable.